PROJECT SUMMARY Pneumococcal pneumonia is a major killer of children worldwide. Acute lower respiratory infection (ALRI) causes up to 15% of early childhood deaths annually. Some pediatric populations, such as children in Papua New Guinea (PNG), suffer more severe ALRI than others. Most ALRI in PNG children is pneumococcal in origin. While increased ALRI severity may be attributed to environmental factors, we hypothesized that some populations could harbor genetic variants that increase susceptibility. By sequencing pediatric cases of pneumococcal ALRI and control samples, we identified a single nucleotide variant (SNV) in the gene COQ6 that may underlie severe pneumococcal ALRI susceptibility. COQ6 encodes coenzyme q6, which is required to synthesize CoQ, a membrane lipid enriched in mitochondria that has a critical function in cellular ATP generation. Reduced CoQ has been reported in critically ill patients, and CoQ-associated metabolic defects may underlie diverse disease states, such as metabolic syndrome and Parkinson's disease. COQ6, like all enzymes in the CoQ biosynthetic pathway, is highly conserved from yeast to mammals. Thus, the SNV, which converts a conserved aspartate to a tyrosine (D?Y) residue, occurs in a biosynthetic pathway essential to mitochondrial bioenergetics, disruption of which results in multiple pathophysiological conditions. We generated two model systems to show that the D?Y coding change (termed COQ6D?Y) results in dysfunctional COQ6. First, yeast expressing only the human COQ6D?Y cannot use glycerol as a carbon source, while control yeast expressing the wild-type human COQ6 can, indicating that COQ6D?Y impairs CoQ production and thus mitochondrial ATP production. Second, we generated a new mouse model, using CRISPR to introduce the analogous D?Y SNV into the conserved endogenous murine Coq6 locus. Animals have been back-crossed, and homozygous Coq6D?Y mice from two founder lines exhibited increased mortality and increased bacterial dissemination following lung infection with pneumococcus. We therefore have strong preliminary data suggesting that the COQ6D?Y SNV contributes to increased severity of pneumococcal ALRI in children. In Aim 1, we will use our established yeast model to elucidate how COQ6D?Y disrupts CoQ biosynthesis. In Aim 2, we will i) use our established mouse model to define the pathophysiological effects of Coq6D?Y on the host immune response and on lung tissue, ii) test whether Coq6D?Y impacts the function of hematopoietic cells, non-hematopoietic cells, or both, and iii) test if exogenous therapy with CoQ can rescue mice expressing Coq6D?Y during pneumococcal infection. Completion of this proposal will support a future R01 application probing the molecular mechanism by which COQ6D?Y disrupts CoQ biosynthesis and therefore mitochondrial metabolism ? providing fundamental knowledge applicable to diverse diseases. This study will also lay the groundwork essential to developing new adjunctive therapies to improve ALRI outcomes in pediatric populations.